Accelerometer microsensors are commonly employed to measure the second derivative of displacement with respect to time. In particular, linear accelerometers measure linear acceleration along a particular sensing axis and generate an output signal (e.g., voltage) proportional to the linear acceleration. Linear accelerometers are employed for use in vehicle control systems to control safety-related devices on an automotive vehicle, such as frontal and side air bags. Additionally, low-g accelerometers are employed in automotive vehicles for active vehicle dynamics control and suspension control applications.
Conventional linear accelerometers typically employ an inertial mass suspended from a frame by multiple support beams. The inertial mass, support beams, and frame generally act as a spring mass system, such that the displacement of the inertial mass is proportional to the linear acceleration applied to the frame. The displacement of the mass generates a voltage proportional to linear acceleration, which is used as a measure of the linear acceleration.
Many microsensors are capacitive type sensing devices that employ a capacitive coupling between fixed and movable capacitive plates, in which the movable plates move in response to linear acceleration along a sensing axis. One example of a linear accelerometer microsensor is disclosed in U.S. Pat. No. 6,761,070, entitled “MICROFABRICATED LINEAR ACCELEROMETER,” which is hereby incorporated herein by reference. The aforementioned linear accelerometer is generally fabricated by employing micro-electro-mechanical systems (MEMS) fabrication techniques, such as etching and micromachining processes. The linear accelerometer is configured such that the accelerometer detects acceleration in the direction of a single sensing axis.
Active vehicle control and safety systems employed onboard vehicles are becoming increasingly complex and sophisticated. The inclusion of both frontal and side air bags in a vehicle requires an increased number of axes along which acceleration must be sensed. With complex vehicle motions, it is desirable for such systems to employ acceleration sensing devices that can sense acceleration in multiple sensing axes, such as two orthogonal axes (e.g., longitudinal axis and lateral axis).
Conventional dual-axis acceleration sensing systems include the use of two individual single axis accelerometers positioned in close proximity to one another and oriented ninety degrees (90°) relative to each other. The first accelerometer senses acceleration in a first sensing axis and the second accelerometer senses acceleration in a second sensing axis orthogonal thereto. The use of two separate accelerometers requires duplicate components including two separate inertial masses and supporting structures and a large number of interconnects. Additionally, the conventional arrangement of two separate accelerometers exhibits poor mechanical cross axis sensitivity response due to the difference in the center of mass of the two separate inertial masses.
The conventional approach to achieving dual-axis linear acceleration sensing generally suffers from various drawbacks including separate duplicative components, large size, in addition to the inability of some sensing systems to detect acceleration at angles between the first and second sensing axes. It is therefore desirable to provide for a low-cost and compact accelerometer that senses acceleration in multiple sensing axes, and offers enhanced sensitivity that eliminates or reduces the drawbacks of prior known acceleration sensing techniques. It is further desirable to provide for a processing circuit and method of processing the sensor generated signals to extract the measured acceleration in multiple sensing axes.